Emerson AE4-1395 User Manual

5

© 2012 Emerson Climate Technologies, Inc.

Printed in the U.S.A.

Application Engineering

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Compressor operation during the loaded state should 

always be inside of the envelope. The envelopes 

represent allowable operation of the compressor with 

20F° suction superheat at rated voltage. If the specified

modulation ranges are exceeded, overheating of the 

compressor and tripping of the overload can occur 

because of inadequate motor cooling. 

Solenoid Valve and Coil
The  external  solenoid  valve  and  coil  specified  by

Emerson must be used since this is a critical component 

for the proper functioning of this compressor. The 

solenoid valve and coil are designed for approximately 

32 million cycles. Do not attempt to substitute 

replacement coils or valves; use only the replacement 

parts  specified  in

Table 4.  Refer to the Service 

Procedures section for information on changing the 

modulation valves.

Pressure Fluctuations
During scroll modulation the suction and the discharge 

pressure  will  fluctuate.  This  fluctuation  should  be

observed during unit testing. The installation and setting 

of pressure controls should take this into account. 

During the unloaded state, the discharge pressure will 

decrease and the suction pressure will increase. This 

normal  pressure  fluctuation  has  had  no  observable

effect on the reliability of system components, however, 

component manufacturers should be consulted to 

ensure the proper application of their products.

Piping
Unlike a variable speed compressor whose mass flow

and gas velocity changes with its speed, the digital 

scroll’s pumping capacity is equal to its 100% capacity 

while it is pumping. For this reason the gas velocity 

remains high even during periods when the capacity 

demand is low. Because the mass flow and gas velocity

remain high, piping may be designed as if it were 

designed for a non capacity controlled compressor. For 

vertical piping a trap every 20 feet should be sufficient

to ensure proper oil return. This recommendation is 

based upon a minimum 1500 fpm velocity or higher. 

When the digital scroll compressor is part of a tandem, 

a double riser should be considered to assure that the 

velocity remains above 1500 fpm when only the digital 

scroll is running. 

Start Up and Shut Down
To improve the starting characteristics of the digital 

scroll compressor, the the Emerson controllers delay 

loading the compressor for 0.1 seconds. Likewise, to 

eliminate the reverse rotation sound at shut down the 

compressor is unloaded 0.5 seconds before shut down.

Compressor Cycling
Because of the digital scroll's seamless capacity 

modulation from 10% to 100%, capacity short cycling 

should not be a problem for single compressors. 

However, if the digital compressor is in tandem with a 

non modulated scroll, short cycling of the non modulated 

compressor may be a problem if the system control is 

not designed and set correctly. The Emerson digital 

controllers have a built in two minute anti-short cycle 

timer to prevent short cycling.

Sound Characteristics 
The sound spectrum of the loaded state and the 

unloaded state are different. 

be applied to the compressor. Fabricating Services 

(www.fabsrv.com) is a one source for scroll compressor 

sound blankets.

The Emerson controllers unload the compressor a 

fraction of a second before shut down allowing the scroll 

set to unload, ensuring a relatively quiet shutdown.

High Pressure Control 
As mentioned above, not all digital scrolls have IPR 

valves, therefore high pressure controls are required 

in some applications. The recommended maximum cut 

out setting is 425 psig (30 bar) for R-407C & R-22 and 

650 psig (45 bar) for R-410A. The high pressure control 

should have a manual reset feature for the highest 

level of system protection. This pressure control must 

act independently of the digital compressor controller.

Low Pressure Control
Air-conditioning units can be protected against high 

discharge temperatures through a low pressure control in 

the suction line. Testing has shown that a cut out setting 

of not lower than 55 psig (3.8 bar) for R-410A and 25 

psig (1.7 bar) for R-407C & R-22 will adequately protect 

the compressor against overheating from loss of charge, 

blower failure in a TXV system, etc. A higher level of 

protection is achieved if the low pressure control is set to 

cut out at 95 psig (6.7 bar) for R-410A and 55 psig (3.8